Brain abscess
Encyclopedia
Brain abscess is an abscess
Abscess
An abscess is a collection of pus that has accumulated in a cavity formed by the tissue in which the pus resides due to an infectious process or other foreign materials...

 caused by inflammation and collection of infected material, coming from local (ear infection, dental abscess, infection of paranasal sinus
Paranasal sinus
Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity , above and between the eyes , and behind the ethmoids...

es, infection of the mastoid air cells of the temporal bone, epidural abscess) or remote (lung
Human lung
The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately of airways and 300 to 500 million alveoli, having a total surface area of about in...

, heart
Human heart
The human heart is a muscular organ that provides a continuous blood circulation through the cardiac cycle and is one of the most vital organs in the human body...

, kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

 etc.) infectious sources, within the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

 tissue. The infection may also be introduced through a skull fracture following a head trauma or surgical procedures. Brain abscess is usually associated with congenital heart disease in young children. It may occur at any age but is most frequent in the third decade of life.

Deadly brain abscesses due to infection caused from tongue piercing
Tongue piercing
A tongue piercing is a body piercing usually done directly through the center of the tongue, and is the most popular piercing site in the western world after the ear and nostril.-History and culture:...

s have occurred.

Features

The symptoms of brain abscess are caused by a combination of increased intracranial pressure
Intracranial pressure
Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...

 due to a space-occupying lesion (headache, vomiting, confusion, coma
Coma
In medicine, a coma is a state of unconsciousness, lasting more than 6 hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions. A person in a state of coma is described as...

), infection (fever, fatigue etc.) and focal neurologic brain tissue damage (hemiparesis
Hemiparesis
Hemiparesis is weakness on one side of the body. It is less severe than hemiplegia - the total paralysis of the arm, leg, and trunk on one side of the body. Thus, the patient can move the impaired side of his body, but with reduced muscular strength....

, aphasia
Aphasia
Aphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....

 etc.). The most frequent presenting symptoms are headache, drowsiness, confusion
Mental confusion
Confusion of a pathological degree usually refers to loss of orientation sometimes accompanied by disordered consciousness and often memory Confusion (from Latin confusĭo, -ōnis, noun of action from confundere "to pour together", also "to confuse") of a pathological degree usually refers to loss...

, seizure
Seizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...

s, hemiparesis
Hemiparesis
Hemiparesis is weakness on one side of the body. It is less severe than hemiplegia - the total paralysis of the arm, leg, and trunk on one side of the body. Thus, the patient can move the impaired side of his body, but with reduced muscular strength....

 or speech difficulties together with fever with a rapidly progressive course. The symptoms and findings depend largely on the specific location of the abscess in the brain. An abscess in the cerebellum, for instance, may cause additional complaints as a result of brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...

 compression and hydrocephalus
Hydrocephalus
Hydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...

. Neurological examination
Neurological examination
A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired...

 may reveal a stiff neck in occasional cases (erroneously suggesting meningitis). The famous triad of fever, headache and focal neurologic findings are highly suggestive of brain abscess.

Bacterial

Anaerobic and microaerophilic cocci and gram-negative and gram-positive anaerobic
Anaerobic infection
Anaerobic infections are caused by anaerobic bacteria. Anaerobic bacteria do not grow on solid media in room air ; facultative anaerobic bacteria can grow in the presence as well as in the absence of air. Microaerophilic bacteria do not grow at all aerobically or grow poorly, but grow better under...

 bacilli are the predominate bacterial isolates. Many brain abscesses are polymicrobical. The predominant organisms include: Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...

, aerobic and anaerobic streptococci (especially Streptococcus intermedius
Streptococcus intermedius
Streptococcus intermedius is a commensal bacterium and a member of the Streptococcus anginosus group. The S. anginosus group, occasionally termed “Streptococcus milleri group” display hemolytic and serologic diversity, yet share core physiological traits. Despite being commensal organisms, members...

), Bacteroides
Bacteroides
Bacteroides is a genus of Gram-negative, bacillus bacteria. Bacteroides species are non-endospore-forming, anaerobes, and may be either motile or non-motile, depending on the species. The DNA base composition is 40-48% GC. Unusual in bacterial organisms, Bacteroides membranes contain sphingolipids...

, Prevotella
Prevotella
Prevotella is a genus of bacteria.Bacteroides melaninogenicus has recently been reclassified and split into Prevotella melaninogenica and Prevotella intermedia....

, and Fusobacterium
Fusobacterium
Fusobacterium is a genus of filamentous, anaerobic, Gram-negative bacteria, similar to Bacteroides.Fusobacterium contribute to several human diseases, including periodontal diseases, Lemierre's syndrome, and topical skin ulcers...

species, Enterobacteriaceae, Pseudomonas
Pseudomonas
Pseudomonas is a genus of gammaproteobacteria, belonging to the family Pseudomonadaceae containing 191 validly described species.Recently, 16S rRNA sequence analysis has redefined the taxonomy of many bacterial species. As a result, the genus Pseudomonas includes strains formerly classified in the...

species, and other anaerobes. Less common organisms include: Haemophillus influenzae, Streptococcus pneumoniae and Neisseria meningitides.

Bacterial abscesses rarely (if ever) arise de novo within the brain, although establishing a cause can be difficult in many cases. There is almost always a primary lesion elsewhere in the body that must be sought assiduously, because failure to treat the primary lesion will result in relapse. In cases of trauma, for example in compound skull fractures where fragments of bone are pushed into the substance of the brain, the cause of the abscess is obvious. Similarly, bullets and other foreign bodies may become sources of infection if left in place. The location of the primary lesion may be suggested by the location of the abscess: infections of the middle ear result in lesions in the middle
Middle cranial fossa
The middle fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest....

 and posterior
Posterior cranial fossa
The posterior cranial fossa is part of the intracranial cavity, located between the foramen magnum and tentorium cerebelli. It contains the brainstem and cerebellum.This is the most inferior of the fossae. It houses the cerebellum, medulla and pons....

 cranial fossae; congenital heart disease with right-to-left shunts often result in abscesses in the distribution of the middle cerebral artery
Middle cerebral artery
-External links:*...

; and infection of the frontal
Frontal sinus
Sinuses are mucosa-lined airspaces within the bones of the face and skull. The frontal sinuses, situated behind the superciliary arches, are absent at birth, but are generally fairly well developed between the seventh and eighth years, only reaching their full size after puberty...

 and ethmoid
Ethmoid sinus
The ethmoid sinus is each of the two paranasal sinuses within the ethmoid bone, comprising the ethmoidal air cells and filled with air. These are divided into anterior, middle and posterior group. The ethmoidal air cells consist of numerous thin-walled cavities situated in the ethmoidal labyrinth...

 sinuses usually results in collection in the subdural sinuses.

Other organisms

Fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 and parasites may also cause the disease. Fungi and parasites are especially associated with immunocompromised patients. Other causes include: Nocardia asteroides
Nocardia asteroides
Nocardia asteroides is a species of Nocardia.It can cause Nocardiosis, a severe pulmonary infection in immunocompromised hosts....

, Mycobacterium, Fungi (e.g. Aspergillus
Aspergillus
Aspergillus is a genus consisting of several hundred mold species found in various climates worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli...

, Candida, Cryptococcus
Cryptococcus
Cryptococcus is a genus of fungus. Species grow in culture as yeasts. The perfect forms or teleomorphs of Cryptococcus species are filamentous fungi in the genus Filobasidiella...

, Mucorales, Coccidioides, Histoplasma capsulatum, Blastomyces dermatitidis, Bipolaris, Exophiala dermatitidis, Curvularia pallescens, Ochroconis gallopava, Ramichloridium mackenziei, Pseudallescheria boydii), Protozoa (e.g. Toxoplasma gondii
Toxoplasma gondii
Toxoplasma gondii is a species of parasitic protozoa in the genus Toxoplasma. The definitive host of T. gondii is the cat, but the parasite can be carried by many warm-blooded animals . Toxoplasmosis, the disease of which T...

, Entamoeba histolytica
Entamoeba histolytica
Entamoeba histolytica is an anaerobic parasitic protozoan, part of the genus Entamoeba. Predominantly infecting humans and other primates, E. histolytica is estimated to infect about 50 million people worldwide...

, Trypanosoma cruzi
Trypanosoma cruzi
Trypanosoma cruzi is a species of parasitic euglenoid trypanosomes. This species causes the trypanosomiasis diseases in humans and animals in America...

, Schistosoma
Schistosoma
A genus of trematodes, Schistosoma, commonly known as blood-flukes and bilharzia, includes flatworms which are responsible for a highly significant parasitic infection of humans by causing the disease schistosomiasis, and are considered by the World Health Organization as the second most...

, Paragonimus), and Helminths (e.g. Taenia solium). Organisms that are most frequently associated with brain abscess in patients with AIDS
AIDS
Acquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the human immunodeficiency virus...

 are poliovirus
Poliovirus
Poliovirus, the causative agent of poliomyelitis, is a human enterovirus and member of the family of Picornaviridae.Poliovirus is composed of an RNA genome and a protein capsid. The genome is a single-stranded positive-sense RNA genome that is about 7500 nucleotides long. The viral particle is...

, Toxoplasma gondii
Toxoplasma gondii
Toxoplasma gondii is a species of parasitic protozoa in the genus Toxoplasma. The definitive host of T. gondii is the cat, but the parasite can be carried by many warm-blooded animals . Toxoplasmosis, the disease of which T...

, and Cryptococcus neoformans
Cryptococcus neoformans
Cryptococcus neoformans is an encapsulated yeast that can live in both plants and animals. Its teleomorph is Filobasidiella neoformans, a filamentous fungus belonging to the class Tremellomycetes. It is often found in pigeon excrement....

, though in infection with the latter organism, symptoms of meningitis
Meningitis
Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...

 generally predominate.

These organisms are associated with certain predisposing conditions:
  • Sinus and dental infections—Aerobic and anaerobic streptococci, anaerobic gram-negative bacilli (e.g. Prevotella, Porphyromonas, Bacteroides), Fusobacterium, S. aureus, and Enterobacteriaceae
  • Penetrating trauma—S. aureus, aerobic streptococci, Enterobacteriaceae, and Clostridium spp.
  • Pulmonary infections—Aerobic and anaerobic streptococci, anaerobic gram-negative bacilli (e.g. Prevotella, Porphyromonas, Bacteroides), Fusobacterium, Actinomyces, and Nocardia
  • Congenital heart disease—Aerobic and microaerophilic streptococci, and S. aureus
  • HIV infection—T. gondii, Mycobacterium, Nocardia, Cryptococcus, and Listeria monocytogenes
  • Transplantation—Aspergillus, Candida, Cryptococcus, Mucorales, Nocardia, and T. gondii
  • Neutropenia—Aerobic gram-negative bacilli, Aspergillus, Candida, and Mucorales

Diagnosis

The diagnosis is established by a computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...

 (CT) (with contrast) examination. At the initial phase of the inflammation (which is referred to as cerebritis), the immature lesion does not have a capsule and it may be difficult to distinguish it from other space-occupying lesions or infarcts of the brain. Within 4–5 days the inflammation and the concomitant dead brain tissue are surrounded with a capsule, which gives the lesion the famous ring-enhancing lesion
Ring-enhancing lesion
A ring-enhancing lesion is an abnormal finding on CT scan obtained using radiocontrast. On the image there is an area of decreased density surrounded by a bright rim from concentration of the enhancing contrast dye. This can be a finding in numerous disease states...

 appearance on CT examination with contrast (since intravenously applied contrast material can not pass through the capsule, it is collected around the lesion and looks as a ring surrounding the relatively dark lesion). Lumbar puncture
Lumbar puncture
A lumbar puncture is a diagnostic and at times therapeutic procedure that is performed in order to collect a sample of cerebrospinal fluid for biochemical, microbiological, and cytological analysis, or very rarely as a treatment to relieve increased intracranial pressure.-Indications:The...

 procedure, which is performed in many infectious disorders of the central nervous system is contraindicated in this condition (as it is in all space-occupying lesions of the brain) because removing a certain portion of the cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...

 may alter the concrete intracranial pressure balances and causes the brain tissue to move across structures within the skull (brain herniation
Brain herniation
Brain herniation, also known as cistern obliteration, is a deadly side effect of very high intracranial pressure that occurs when the brain shifts across structures within the skull...

).

Ring enhancement may also be observed in cerebral hemorrhages (bleeding) and some brain tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

s. However, in the presence of the rapidly progressive course with fever, focal neurologic findings (hemiparesis, aphasia etc.) and signs of increased intracranial pressure, the most likely diagnosis should be the brain abscess.

Treatment

The treatment includes lowering the increased intracranial pressure and starting intravenous antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

s (and meanwhile identifying the causative organism mainly by blood culture studies).

Surgical drainage of the abscess remains part of the standard management of bacterial brain abscesses. The location and treatment of the primary lesion also crucial, as is the removal of any foreign material (bone, dirt, bullets, and so forth).

There are few exceptions to this rule: Haemophilus influenzae
Haemophilus influenzae
Haemophilus influenzae, formerly called Pfeiffer's bacillus or Bacillus influenzae, Gram-negative, rod-shaped bacterium first described in 1892 by Richard Pfeiffer during an influenza pandemic. A member of the Pasteurellaceae family, it is generally aerobic, but can grow as a facultative anaerobe. H...

 meningitis is often associated with subdural effusions that are mistaken for subdural empyemas. These effusions resolve with antibiotics and require no surgical treatment. Tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

 can produce brain abscesses that look identical to conventional bacterial abscesses on CT imaging. Surgical drainage or aspiration is often necessary to identify Mycobacterium tuberculosis
Mycobacterium tuberculosis
Mycobacterium tuberculosis is a pathogenic bacterial species in the genus Mycobacterium and the causative agent of most cases of tuberculosis . First discovered in 1882 by Robert Koch, M...

, but once the diagnosis is made no further surgical intervention is necessary.

Prognosis

It was once fatal before the CT era, now, if the abscess is treated before the person goes into a coma, then the death rate has been estimated from 5% to 20% although it is greater in cases of multiple abscesses, when raised intracranial pressure is observed and depending on the level of neurological dysfunction on presentation. Early treatment and the patients overall health has an effect on prognosis. Other factors include: antibiotic resistance or the abscess location. An abscess deep within the brain is more difficult to treat than others.

External links

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